Low-intensity infrared heating systems comprise one or more burners feeding hot gaseous effluent into an emitter tube which, as a result of the heat of the effluent, emits energy in the infrared range. When used in combination with a suitable reflector, and typically, but not necessarily, placed overhead in a building structure, such as a warehouse or production area the low-intensity infrared system provides efficient, comfortable and highly effective heating through directionalized or focussed radiation. The effectiveness of such systems in providing comfort derives from a number of factors including the ability to direct the radiation to relatively specific areas where it is needed and desired and also from the fact that humans and animals feel more comfortable at lower air temperatures when expose to radiant heat than when they are in higher temperature air heated and circulated by a conventional furnace. Additionally, the concrete floors of industrial and agricultural buildings absorb radiation from the emitter tube and thereafter release heat at floor level. The result is substantially lower cost of operation and increased comfort to persons working in the area and, in some agricultural, horticultural and commercial applications such as greenhouses, hog barns and chicken coops, increased continued growth and shorter incubation times which also results in lower costs.
The temperature of the emitter tube and, hence, the magnitude of the radiation produced thereby, typically varies from a maximum immediately downstream of the burner to a minimum at the exhaust. In a prior art system, the maximum or inlet temperature may be on the order of 1000.degree. F. and the low or exhaust temperature may be about 170.degree. F. The minimum temperature is preferably selected to be high enough to avoid condensation of acids within the system thereby to prevent corrosion at or near the exhaust end.
Because of the high temperature gradient, i.e., about 830.degree. F., along the emitter tube and the relatively high temperatures often needed near the input end to achieve system capacity specifications, it is often necessary to provide large spacings between the emitter tube and such things as combustible building materials and fuel tanks to satisfy safety requirements. Moreover, very hot emitters can be uncomfortable to stand under if spacings are under 8 feet or so. Ultimately, the spacing requirement affects building space utilization efficiency; e.g., lower ceilings can reduce construction costs.
One approach to providing a more uniform radiant energy output along the length of the emitter tube is described in my U.S. Pat. No. 4,529,123 issued July 16, 1985, "Radiant Heater System." In that patent I disclosed the use of a ceramic insert near the burner end of the tube to reduce tube temperature and effectively transfer energy downstream in the system.